Device for dosing a liquid preparation

ABSTRACT

An injection device is provided for a continuously variable metering and administering of a liquid preparation and having a holder device for a multi-dose injection cartridge, the rear piston of which may be moved forward by means of a piston rod. The piston rod is provided with releasable locking means having at least one longitudinal groove having a wedge-shaped cross section and at least one locking lug having a cross section adapted to that of the groove, and means for urging the locking lug into said grooves to lock the movement of the piston rod, or to release the locking lug from said groove to free the movement of said piston rod. At its rear end, the piston rod is connected to a spring device for moving the piston rod forward and to a device for determining the stroke of the piston rod when the preparation is administered.

DESCRIPTION

1. Technical Field

The present invention is directed to a device for dosing andadministering a liquid preparation. More specifically, the inventionrefers to repeated dosing and administering of liquid pharmaceuticpreparations by parenteral injection from a multi-dose container. Stillmore specifically, the invention refers to a device for infinitelyvariable dosing and administering of liquid pharmaceutic preparation byparenteral injection from a multi-dose container, such as an injectioncartridge.

2. Background Art

International patent application PCT/SE92/00654 describes a method forrepeated dosing of a liquid preparation of a pharmaceutically activeagent by administration from a multi-dose container having a definedvolume. What characterizes this method is that the amount of thepreparation to be dosed is selected to be 1/N of the volume of themulti-dose container, N being an integer having a value of 2 or higher.The value of N is selected and set before the repeated dosing of thepreparation from the multi-dose container is started, and is maintainedunchanged through a series of N successive administrations from themulti-dose container, which has consequently then been emptied. As asecond variable or degree of freedom is used the concentration of theliquid preparation, such that the portion 1/N will give the desired doseof the pharmaceutically active agent. By using a series of containerswith preparations of different concentrations, and a plurality of valuesfor N, it is clear that a great number of different doses of the activeagent can be obtained.

Through the method and system described, it has thus become possible toadminister a number of doses of a liquid preparation from a multi-dosecontainer in such a way that essentially no residue of the preparationis obtained. This is of considerable importance when very expensivepharmaceutical agents are to be administered, such as growth hormones.

The above-mentioned international application PCT/SE92/00654 alsodiscloses a device for the repeated dosing of a liquid preparation froma multi-dose container. Such a device comprises a holder device for amulti-dose container having a defined volume and containing apreparation having a defined composition, and the multi-dose containeris provided with a fixed front wall, through which may be arranged anoutlet for the preparation, and a movable rear wall, which may act as apiston for expelling the preparation through said outlet, and a pistonrod, by which the rear movable wall may be urged forwards. Whatcharacterizes the device is that the piston rod is provided withreleasable blocking means by which the forward movement of it is limitedto a predetermined length, which corresponds to a forward movement ofthe rear movable wall corresponding to 1/N of the multi-dose container,N being an integer having a value of 2 or higher.

It is to be noted that in the following specification and claims, theexpressions "front" and "forward" refer to the direction in which theliquid preparation is made to flow when it is administered. Conversely,the opposite direction is denoted as "rear" and "rearward",respectively.

In a preferred embodiment of the device described above, it comprises abarrel for holding at its front end part an injection cartridge and apiston rod for actuating said injection cartridge to expel a set amountof the liquid preparation from the cartridge. The releasable blockingmeans comprise a fixed chuck and a movable chuck which clamp around thepiston rod through the action of a spring force, said clamping actionbeing releasable by reducing said spring force. Thus, the front chuck isfixed in relation to the barrel and the cartridge, and its clampingaction around the piston rod may be actuated to lock it securely to thechuck, or may be released to allow the piston rod to move in relation tothe chuck. The rear chuck is movable in relation to the barrel and thecartridge, and can be moved along the piston rod, when its clampingaction is released, or may follow the piston rod in its movement, whenthe clamping action is actuated.

When a measured dose of the liquid preparation is to be administered,the rear chuck is moved rearwards against a spring force by means of ayoke arrangement, which at the same time releases the clamping action ofthe chuck such that it can move along the piston rod at the same time assaid piston rod is locked in place by means of the clamping action ofthe front chuck. The rearward movement of the rear chuck is limited bystopping means, and the clamping action of this chuck is actuated againin this rear position, so that the chuck is locked in place in said rearposition. The distance that the rear chuck is moved rearward ispredetermined and set in the device, and determines the magnitude of thedose of the liquid preparation.

When a dose is to be administered, the clamping action of the frontchuck is released. The spring force will now urge the rear chuck and thepiston rod forward the same distance as that set for the rearwardmovement. Under the influence of the spring force, the piston rod willact on the rear movable wall of the injection cartridge to urge saidwall forward to expel a metered dose of the liquid preparation from thecartridge.

These two readying and administering steps may then be repeated as manytimes as desired, until the cartridge has been emptied.

The important feature of the device described above is that the dose setcan be infinitely varied. This is necessary for administring inaccordance with the method described, where no residue should be leftafter administering a determined number of doses. This method and deviceshould not be confused with the prior art methods and devices foradministering liquid preparations. The prior art devices for repeatedadministration from a multi-dose cartridge usually consist of aninjection device which comprises a mechanism for a stepwise forwardmovement of the rear movable wall of the injection cartridge, such as ascrew or ratchet mechanism. The steps which are possible with this typeof mechanism are fixed and a dose can only be determined by a givennumber of steps. Thus, the prior art mechanism may be adapted to theinjection cartridge in such a manner that an advancement of themechanism by one step will give a dosed amount of, for example, 1/8 ofthe volume of the cartridge. However, the mechanism cannot the be easilyadapted to give a dose of, for example, 1/7, 1/9 or 1/10 of the volumeof the cartridge. This means that only a limited number of dose amountsare possible without giving a residue.

In contrast to this, it will always be possible with the devicedescribed above to set a dose which is 1/N of the volume of thecartridge, N being an integer. The value of N may be set on the devicebefore a series of administrations is started, and it cannot then beeasily changed. By providing a suitable range of cartridges with varyingconcentrations of the preparation and a suitable range of values for N,it is possible to obtain a wide range of possible doses. This range ofdoses may then be presented in a table, from a computer memory, or in anomograph, for easy reference by the physician.

The device described in the international patent applicationPCT/SE92/00654 has turned out to work well in the practice of the methoddescribed. However, there is room for some improvements. Thus, thearrangement of two separate chucks for alternately locking and releasingthe piston rod is rather complicated. A considerable spring force isnecessary to grip and lock the piston rod securely, and this also makesit necessary to use a considerable force when the chucks are to bereleased, such as when an injection is to be administered. This may makethe administering difficult in those cases when the patient is toadminister the injections to himself, such as in the ambulatorytreatment of diabetes with insulin. After repeated use with a number ofinjection cartridges, this may also lead to wear on the piston rod, suchthat the accuracy of the metering of the dose will be decreased.

These disadvantages are eliminated by the injection device of thepresent invention.

SUMMARY OF THE INVENTION

According to the present invention, an injection device is provided foran infinitely or continuously variable metering and administering of aliquid preparation, and comprising a holder device for a multi-doseinjection cartridge which comprises a fixed front wall through which maybe arranged a liquid connection for discharging the preparation, and arear, movable wall which may be moved forward by means of a piston rodto expel the preparation from the cartridge. What characterizes theinvention is that the piston rod is provided with releasable lockingmeans, having at least one longitudinal groove having a wedge-shapedcross-section, and at least one locking lug having a cross-sectionadapted to that of the groove, and means for urging the locking lug orlugs into the groove or grooves to lock the longitudinal movement of thepiston rod, and to release the urging to free the piston rod, and thatthe piston rod at its rear end is connected to a spring device formoving the piston rod forward at the administering, and a device forsetting the stroke of the piston rod when the preparation isadministered.

In a preferred embodiment, the piston rod is provided with at least twolongitudinal grooves which are evenly spaced around the circumference ofsaid piston rod, and a corresponding number of locking lugs. Aroundtheir outer circumference, the lugs have a conical shape and aresurrounded by a tubular sleeve, which rests against the outer conicalparts of the locking lugs and can be moved in the longitudinaldirection, such that by this movement it can exert a pressure againstthe locking lugs and urge them into the grooves to lock the piston rod,or release the pressure on the locking lugs to free the piston rod.

In a still further preferred embodiment, the tubular sleeve is pressedagainst the locking lugs by means of a spring pressure in thelongitudinal direction, to urge the locking lugs into the grooves. Bymeans of a lever device, the tubular sleeve may be displaced in thelongitudinal direction against the spring pressure to release thepressure on the locking lugs, to free the piston rod.

BRIEF DESCRIPTION OF DRAWINGS

In the drawings, FIG. 1 shows an injection device according to theinvention before it has been readied for an injection. FIG. 2 shows thedevice after it has been readied for an injection. FIG. 3 shows thedevice after an injection has been administered. FIG. 4 shows asectional view along the line IV--IV in FIG. 1. FIG. 5 shows a view inperspective of the locking arrangement for the piston rod. In all thefigures, like parts have the same reference numbers.

BEST AND VARIOUS MODES FOR CARRYING OUT INVENTION

FIG. 1 of the drawings shows a sectional view of an injection deviceaccording to the invention. The device comprises a holder, whichcomprises a rear sleeve 1 and a front sleeve, which in the embodimentshown consists of two joined sleeves 2 and 3. These three sleeves arejoined together by means of threads 4 and 5, respectively, to hold aninjection cartridge 6, which in its turn is secured by an interiorsleeve 7, which is joined to the front sleeve 3 by means of the thread8.

The injection cartridge 6 is of a conventional design and has abottleneck-shaped front end 9. This front end 9 is provided with aconventional end closure or wall, which usually comprises a rubberseptum which is held in place by a metal capsule which has an opening inits center part, where the septum is exposed. Through this opening, aneedle may be inserted through the septum to provide a liquid connectionwith the interior of the cartridge and an outlet for the liquidpreparation inside the cartridge. As the arrangements at the front endof the cartridge are of a completely conventional nature, they are notshown in detail.

The chamber 10 of the cartridge 6 contains a liquid preparation and isclosed at its rear end by a movable wall or piston 11, which is actuatedby a piston rod 12.

The piston rod 12 is provided with three longitudinal grooves 13, whichhave a wedge-shaped cross-section. This can be seen more clearly in FIG.4, which is a cross-sectional view along IV--IV in FIG. 1. These groovesextend along the whole length of the piston rod, except for its rear endpart.

In the longitudinal grooves 13 are arranged three locking lugs 14, whichalso have a wedge-shaped cross-section adapted to that of the grooves13. This can be seen more clearly in FIGS. 4 and 5. The lugs 14 aremounted on upright stalks 15 which extend from the rear end of theinterior sleeve 7. These stalks should have a certain springiness, butwill not have to take up any great bending angles. The spring action ofthe stalks 15 will strive to pull the locking lugs 14 out of the grooves13, but this spring force does not have to be very great.

The outer edges 16 of the locking lugs 14 form parts of a circle, andtheir circumferential surfaces are conical with their smaller diameterat the rear, as can be seen in FIGS. 4 and 5. The locking lugs 14 aresurrounded by a tubular actuating sleeve 17, which is arranged outsideof the interior sleeve 7 and coaxially therewith. The rear part of theactuating sleeve 17 has an interior surface 18, which is conical and isadapted to the conical surface 16 of the circumference of the lockinglugs 14, such that the interior surface 18 abuts against the exteriorconical surface 16 of the locking lugs 14. Furthermore, a spring 19 isarranged in a space between the actuating sleeve 17 and the front sleeve2. This spring 19 rests against a shoulder 20 on the actuating sleeve 17and a shoulder 21 on the front sleeve 2 and exerts a pressure on thesetwo shoulders, such that it strives to urge the actuationg sleeve 17forward. By this action, the interior conical surface 18 of theactuating sleeve 17 will press against the exterior conical surface 16of the locking lugs 14, such that these lugs are urged into the grooves13, to securely lock the piston rod and prevent any longitudinalmovement thereof.

This is an important feature of the present invention. By their wedgeaction, the locking lugs 14 will exert considerable pressure against thewalls of the grooves 13 when they are in their locking positions,without the force of the spring 19 acting on the locking lugs 14 throughthe intermediary of the conical surfaces 16 and 18 having to beexcessively great.

The locking action by the lugs 14 on the piston rod 12 may be releasedby moving the actuating sleeve 17 rearward. For this, a lever device 22is arranged through an opening in the front sleeve 2. The lever has anexternal arm 22 and an internal arm 23 and rests on a projection 24,which provides a fulcrum. The end of the internal arm 23 rests against aforward-facing shoulder 25 of the actuating sleeve 17, and through theaction of the spring 19, a contact between the shoulder 25 and theinternal arm 23 of the lever is assured at all times. Thus, when theexternal arm 22 of the lever is moved inwards toward the front sleeve 3,the internal arm 23 will turn about the fulcrum 24 and be displacedrearwards, such that the actuating sleeve 17 is moved rearwards. Theinward-facing surface 18 of the actuating sleeve at its rear end willthen no longer press against the outward-facing surfaces 16 of thelocking lugs 14, which will then no longer be urged against the walls ofthe grooves 13 in the piston rod 12. The piston rod will then be free tomove in relation to the front sleeves 2 and 3 and the injectioncartridge 6.

At its rear end, the piston rod 12 is provided with a transversal flange26 and a coaxial threaded tubular sleeve 27. A screw 28 can be screwedinto the threaded sleeve 27 for a given distance, which determines theamount of the preparation to be administered in a dose, as will beexplained in more detail in the following. The screw 28 is provided witha stopping device 29, which may be shaped as a knurled wheel for easysetting of the dose. However, other shapes are also possible.

In the drawing, the threaded sleeve 27 is shown having an internalthread and the screw 28 as having an external thread. However, it willbe understood that threaded sleeve 27 may instead have an externalthread, in which case the screw 28 will be a sleeve having an internalthread, This will not affect the function of the device.

The rear sleeve 1 is provided at its rear end with a central opening 30,through which the screw 28 can pass, but not the stopping device 29.This opening 30 is connected to an internal rear sleeve 31, whichextends forward from the rear opening 30 for a determined distanceinside the rear sleeve 1. The threaded tubular sleeve 27 at the rear endof the piston rod 12 fits inside the internal rear sleeve 31 and may berotated or displaced longitudinally therein. Between the outer wall ofthe internal rear sleeve 31 and the internal wall of the rear sleeve 1is provided a tubular space, and in this space is arranged a helicalspring 32 between the rear face of the flange 26 and the internal rearend wall of the rear sleeve 1. The force of this spring 32 strives topush the flange 26 and the piston rod 12 forward and provides the forcenecessary for expelling the liquid preparation from the chamber 10 ofthe injection cartridge 6 when an injection is to be administered. Theforward movement of the piston rod, however, is restricted by thestopping device 29, which rests against the rear end of the rear sleeve1, and the possible movement of the piston rod 12 forward is determinedby how far the screw 28 has been screwed into the threaded sleeve 27.

The rear sleeve 1 may be screwed onto the front sleeve 2 by means of thethread 4. When this is done, the piston rod 12 will be moved rearward inrelation to the rear sleeve 1, and the flange at its rear end willapproach the forward edge of the internal rear sleeve 31, and when itabuts this edge, no further movement rearward is possible. As isapparent from the foregoing, the distance that the piston rod 12 can bemoved rearward is determined by how far the screw 28 has been screwedinto the threaded sleeve 27. It is also realized that during thismovement rearward by the piston rod 12, it is locked in place relativeto the injection cartridge 6 and the front sleeves 2 and 3 by thelocking lugs 14, which are being urged into the grooves 13 in the pistonrod by the pressure of the actuating sleeve 17.

FIG. 2 shows the device of the invention after the rear sleeve 1 hasbeen screwed onto the front sleeve 2 in the direction of the arrow 33until the flange 26 at the rear end of the piston rod 12 abuts theforward edge of the internal rear sleeve 31. The spring 32 has beencompressed between the rear face of the flange 26 and the front face ofthe rear end wall of the rear sleeve 1. Through the relative movement ofthe piston rod 12, the threaded sleeve 27 at its rear end and the screw28 with its stopping means 29 now protrude from the rear end of the rearsleeve 1.

The piston rod 12 is still gripped by the locking lugs 14, which areurged into the grooves 13 by the pressure from the inclined surface 18of the actuating sleeve 17. This sleeve is urged forward by the spring19.

FIG. 3 shows the injection device of the invention after an injectionhas been administered. The external arm 22 of the lever device has beenmoved inward, as is shown by the arrow 34, to rotate lever about thefulcrum 24 such that the end of the internal arm 23 has been movedrearward. The internal arm 23 has acted on the shoulder 25 of theactuating sleeve 17 to displace it rearwards against the pressure of thespring 19. This rearward movement of the actuating sleeve 17 will alsomove the interior conical surface 18 at its rear end away from thecorresponding conical surfaces 16 of the locking lugs 14. These lugswill then no more be forced into the grooves 13 to lock the piston rod12, which is now free to move forward under the influence of thecompressed spring 32. As the forward end of the piston rod rests againstthe rear face of the rear movable wall or piston 11, the pressure of thespring 32 will thus displace the piston 11 forward for a given distance,to expel a determined amount of the liquid preparation from the chamber10 of the injection cartridge 6.

The forward travel of the piston rod 12 is stopped when the stoppingmeans 29 at the rear end of the screw 28 abuts the rear end of the rearsleeve 1. It will thus be seen that the amount of the liquid preparationadministered from the injection cartridge 12 is determined by thedistance that the piston rod 12 is moved forwards, and this distance inturn is determined by the distance that the screw 28 has been screwedinto the threaded sleeve 27. It is preferred that the setting of thedose of the injectable preparation is arranged in such a way that thesetting cannot be easily changed. Thus, the arrangement of the screw 28with its stopping means 29 and the threaded sleeve 27 may be providedwith some locking means, so that the dose set by the physician, thepharmacist or by the patient himself cannot be easily changedinvoluntarily. Such means are within the competence of a person skilledin this art.

When the pressure on the external arm 22 of the lever is released, thespring 19 will again act on the shoulder 20 of the actuating sleeve 17to move it forward. The conical surface 18 at its rear end will againget into contact with the conical surfaces 15 of the locking lugs 14, tourge them into the grooves 13 in the piston rod 12. The piston rod 12will now be locked in relation to the injection cartridge 6, and thecomplete device will again be in the state shown in FIG. 1.

FIG. 4 shows a sectional view along the line IV--IV in FIG. 1. It ishere seen how the locking lugs 14 are urged into the grooves 13 of thepiston rod 12, by the action of the rear end of the actuating sleeve 17.The piston rod 12 will now be locked by the wedge action of the lockinglugs 14 being forced into the grooves 13.

FIG. 5 shows a view in perspective of the arrangement of the lockinglugs. For clarity, the piston rod 12 is not shown. It is seen how thelocking lugs 14 are mounted on stalls 15 at the rear end of the interiorsleeve 7 which secures the injection cartridge (not shown). The outerperipheral parts 16 of the locking lugs 14 have a conical shape and aresurrounded by the actuating sleeve 17. At the rear end of this sleeve,its internal wall 18 has a conical shape which is adapted to the shapeof the peripheral parts 16 of the locking lugs 14. Thus it will be seenthat if the actuating sleeve 17 is moved forward, its internal conicalpart 18 at its rear end will abut against the external peripheral parts16 of the locking lugs 14. This axial movement will then be translatedinto a radial movement inward of the locking lugs 14.

In the embodiment shown in the drawings, the device of the invention isintended to be disposable, i.e. there are no provisions for an easyremoval of a finished injection cartridge and the insertion of a freshone. The device is intended to be charged with an injection cartridgewhen it is assembled, and to be discarded after the cartridge has beenemptied. However, it is clear to those skilled in the art that thedevice of the invention may also be designed as a re-usable device, andthe modifications necessary for this are apparent to such skilledpersons. For example, one such modification may be to arrange the frontsleeve 3 in two coaxial tubular parts, which may be screwed into eachother or otherwise assembled. In this way, a finished cartridge may bepulled out forwards, when the front end has been removed, and a freshcartridge be inserted. The two parts of the front sleeve 3 are thenassembled again, and the device may be readied for use.

The function of the device of the invention will now be described indetail:

When the device is to be readied for an injection, it is in the stateshown in FIG. 1 of the drawings. An injection cartridge 6 has beeninserted into the front sleeve 3 and is secured by the interior sleeve8. The front end of the piston rod 12 rests against the rear face of thepiston 11, and the piston rod is secured in place by the locking lugs14, which are forced into the grooves 13 to lock any axial movement ofthe piston rod. The spring 19 urges the actuating sleeve 17 forward, andthe inclined surface at the rear end of this sleeve forces the lockinglugs 14 into the grooves 13.

At the rear end of the piston rod 12, the flange 26 is situated at adistance from the front end of the rear interior sleeve 31. Thisdistance is determined by how far the screw 28 has been screwed into thethreaded tubular sleeve 27. The stopping device 29 rests against therear end of the rear sleeve 1.

To prepare the device for an injection, the user turns the rear sleevein the direction shown by the arrow 33 in FIG. 2. The rear sleeve 1 willthen be screwed onto the front sleeve 2 by means of the thread 4, andthe piston rod 12 with its flange 26 and the threaded tubular sleeve 27with the screw 28 and the stopping device 29 will move rearwards inrelation to the rear sleeve 1. After the rear sleeve 1 has been screwedonto the front sleeve 2 for a predetermined distance, the flange 26 onthe piston rod 12 will abut the front end of the rear interior sleeve31, and no further movement is possible. The screw 28 and the stoppingdevice 29 will now protrude from the opening 30 in the rear end face ofthe rear sleeve 1, and the spring 32 has been compressed.

During this preparation process, the piston rod 12 has been locked inplace by the locking lugs 14, which have been forced into the grooves 13by the action of the spring 19 and the inclined surfaces 16 and 18.Thus, there has been no movement of the piston rod 12 in relation to theinjection cartridge 6.

When the injection is to be administered, the external arm 22 of thelever is moved inwards, as is shown by the arrow 34 in FIG. 3. The leverwill then turn about the fulcrum 24 such that the end of the internalarm 23 will move rearward to act on the shoulder 25 of the actuatingsleeve 17. This sleeve will then be moved rearwards against the pressureof the spring 19, and the conically inclined surface 18 at its rear endwill no longer press against the correspondingly inclined surfaces 16 ofthe locking lugs 14. The locking lugs 14 will then no longer be urgedinto the grooves 13, and through the spring action of the stalks 15, thelocking lugs 14 will withdraw slightly from said grooves 13. The pistonrod 12 will then be free to move forward under the influence of the rearspring 32 and will move the piston 11 forward to expel a predeterminedamount of the injectable preparation from the chamber 10 of theinjection cartridge 6. The forward travel of the piston rod 12 is endedwhen the stopping device 29 abuts the rear end of the rear sleeve 1, andthe distance travelled is determined, as shown in the foregoing, by thedistance that the screw 28 has been screwed into the threaded tubularsleeve 27.

The piston rod 12 will be free as long as the pressure inward on theexternal arm 22 of the lever is maintained. When this pressure isreleased, the actuating sleeve 17 will again move forward by theinfluence of the spring 19, and the inclined surface 18 at the rear endof this sleeve will again exert pressure on the circumferential surfaces15 of the locking lugs 14, forcing them into the grooves 13 to lock thepiston rod 12 in place.

It will be seen that the internal arm 23 of the lever and the actuatingsleeve 17 will not have to be displaced for any great distance to effectthe locking or unlocking, respectively, of the movement of the pistonrod 12. This is a consequence of the wedge effect being utilized, and isan important advantage of the invention.

The device is now again in the state shown in FIG. 1, and the processdescribed above may be repeated until the injection cartridge is empty.

It is to be noted that the injection is administered by means of theforce exerted by the rear spring 32, which means that the device hasauto-injecting properties. Thus, the user only has to insert the needleat the site of injection and push the lever 22 inward, but will not haveto maneuver the piston rod itself to carry out the injection. Thisgreatly simplifies the process of administering the injections, and isan added advantage of the device of the invention.

In the embodiment of the invention shown in the drawings, the injectioncartridge has been shown as a single-chamber cartridge. However, it isclear to those skilled in the art that also dual-chamber cartridges canbe used in the device. Such dual-chamber cartridges comprise twochambers separated by a movable wall or piston. The front chamberusually contains a solid component of the injectable preparation, andthe rear chamber contains a liquid component to dissolve the solidcomponent. When the rear piston of the dual-chamber cartridge is movedforward, the pressure will be transmitted through the largelyincompressible liquid to move the separating wall forward until a bypassconnection between the two chambers is opened. The liquid component willthen flow over into the front chamber to dissolve the solid component,and the solution formed may then be administered as described in theforegoing. Dual-chamber cartridges are well-known and are used forinjectable preparations which are unstable in the form of a solution andtherefore will have to be prepared immediately before theadministration.

The modifications necessary for adapting the device of the invention tothe use of a dual-chamber injection cartridge can easily be determinedby those skilled in the art. When a dual-chamber cartridge is used in adevice of the invention, the user will first make a suitable number of"dry run" administrations to advance the rear piston of the cartridgesufficiently far to urge the liquid component over into the frontchamber of the cartridge. The device is then ready to be used asdescribed in the foregoing. Other processes for mixing the twocomponents prior to injection are also apparent to those skilled in theart.

The design in detail of the device of the invention is within thecompetence of a person skilled in the art, once the inventive idea hasbeen understood. Also ths selection of suitable materials for thevarious parts of the device is no problem for those skilled in the art.Conventionally, such materials as stainless steel, various plastic andrubber materials, and glass are used for the parts of the device. Itgoes without saying that all materials must be able to withstand heatsterilization.

It is to be noted that the expression "liquid injectable preparation" isintended to encompass not only solutions, but also emulsions,suspensions and other dispersions which are pharmaceutically acceptablefor parenteral injection.

Through the present invention, it has been possible to provide a devicefor injection where the dose to be injected may be set in an infinitelyvariable manner, such that the device may be used for administeringinjections in accordance with the system described in the foregoing,where no residues are obtained. This is an important advantage,especially when very expensive preparations are to be administered.

It is to be noted that the embodiments described in the foregoingspecification and drawings are only examples, and are not intended torestrict the scope of the invention in any way. A number ofmodifications and variations are possible and apparent to those skilledin the art, and the invention is only restricted by the scope of theappended claims.

We claim:
 1. An injection device for continuously variable metering andadministering of a liquid injectable preparation, comprising a holderdevice for a multi-dose injection cartridge which comprises a frontfixed wall through which may be arranged a liquid connection fordischarging the preparation, and a rear movable wall which may be movedforward by means of a piston rod to expel the preparation from saidcartridge, characterized in that the piston rod is provided withreleasable locking means consisting of at least one longitudinal groovehaving a wedge-shaped cross-section and at least one locking lug havinga cross-section adapted to that of the groove, and means for urging saidlocking lug into said groove to lock the longitudinal movement of saidpiston rod, and to release said locking lug from said groove to freesaid piston rod, and that the piston rod at its rear end is connected toa spring device for moving said piston rod forward at the administering,and a device for setting the stroke of the piston rod when thepreparation is administered.
 2. An injection device according to claim1, characterized in that said locking means consist of at least twolongitudinal grooves which are evenly spaced around said piston rod, anda corresponding number of locking lugs, said locking lugs having aconical shape around their outer peripheral parts with the smallerdiameter at the rear and being surrounded by a tubular sleeve whichrests against the outer conical parts of said locking lugs and which canbe moved in the longitudinal direction such that it exerts an inwardforce on said locking lugs to urge them into said grooves to lock themovement of the piston rod, or release the force on said locking lugs tofree the movement of said piston rod.
 3. An injection device accordingto claim 2, characterized in that said tubular sleeve is urged againstsaid locking lugs by means of a spring pressure in the longitudinaldirection on said sleeve to urge said locking lugs into said grooves,and that said tubular sleeve by lever means may be displaced in thelongitudinal direction against said spring pressure, to release thepressure on said locking lugs to free the movement of the piston rod. 4.An injection device according to claim 1, characterized in that thepiston rod at its rear end is connected to a threaded coaxial sleevewhich is in engagement with a threaded screw which at its rear end isprovided with a stopping device which after the administering restsagainst the rear end of said holder device, the stroke of said pistonrod being determined by the distance which said screw has been advancedinto said threaded sleeve.
 5. An injection device according to claim 4,characterized in that the holder device for the injection cartridge isprovided at its rear end with an internal forward-facing sleeve whereinthe threaded coaxial sleeve arranged at the rear end of said piston rodis slidably arranged, and that said sleeve at the rear end of saidpiston rod is provided with a flange which by abutting the front end ofsaid internal forward-facing sleeve restricts the forward travel of saidinternal sleeve, and by this also the forward stroke of the piston rodat the administering.
 6. An injection device according to claim 1,characterized in that said holder device comprises a front outer sleeve,which surrounds the injection cartridge and the locking means for thepiston rod, and a rear outer sleeve, which surrounds the spring devicefor moving the piston rod forward at the administering and the devicefor determining the stroke of said piston rod, said front outer sleevebeing arranged to be screwed into said rear outer sleeve such that theinjection device by this movement is readied for injection by moving therear internal forward-facing sleeve forwards against the pressure ofsaid spring until the flange on the sleeve at the rear end of the pistonrod abuts the front end of said internal forward-facing sleeve.
 7. Aninjection device according to claim 2, characterized in that the pistonrod at its rear end is connected to a threaded coaxial sleeve which isin engagement with a threaded screw which at its rear end is providedwith a stopping device which after the administering rests against therear end of said holder device, the stroke of said piston rod beingdetermined by the distance which said screw has been advanced into saidthreaded sleeve.
 8. An injection device according to claim 2,characterized in that said holder device comprises a front outer sleeve,which surrounds the injection cartridge and the locking means for thepiston rod, and a rear outer sleeve, which surrounds the spring devicefor moving the piston forward at the administering and the device fordetermining the stroke of said piston rod, said front outer sleeve beingarranged to be screwed into said rear outer sleeve such that theinjection device by this movement is readied for injection by moving therear internal forward-facing sleeve forwards against the pressure ofsaid spring until the flange on the sleeve at the rear end of the pistonrod abuts the front end of said internal forward-facing sleeve.